2010-04-05

Opportunity Sol 426 (Spirit Sol 446)

Today's my last day on Opportunity for a while, and it's off to an inauspicious start. Our main relay orbiter, Mars Odyssey (ODY), went into safe mode over the weekend. As a result, we didn't get any of our downlink. Not a sausage.

When I look at it the right way, I see our "no news" as good news: I checked in on the rover over the weekend and was alarmed that there had been no updates. I wasn't sure why that would happen, but of course the explanation that immediately occurred to me was that I had killed it. So it's not that, and that's good.

Of course, maybe ODY went into safe mode and I killed Opportunity. Heck, maybe whatever I did to kill Opportunity took ODY with it. ODY learned that Opportunity was gone and then ODY died from grief, maybe. But what are the odds?

Well, if we assume Opportunity is healthy, maybe we can even drive it. Our uplink isn't affected, so we could send up another all-autonav drive sequence. I have it all worked out in my head, and start to pitch the idea. But I'm brought up short by the fact that there's no room in flash: the drive will generate so much data that it will push out other stuff we might not want to discard, and that's a risk we can't take. Plus, nobody seems to know for sure, but several people suspect there's a rule about that: you have to confirm that the rover is healthy before you uplink mobility sequences. (We have someone do that for weekend drives, for instance -- they don't re-plan in the middle, but they can pull the plug on continued driving.) So that idea's out.

So we can't drive, and without images, we can't IDD, either. So you'd think I'd have the day off. But it doesn't work out like that. Instead, I decide to use this unexpected holiday to try to get other work done. I figure if I can get some stuff done for Phoenix today, I won't feel so bad about ignoring them on days when I want to focus on the rovers.

Meanwhile, the ops team has reconfigured the rover to try to send a little data directly down to Earth. This takes lots of power and doesn't return a lot of data, but it'll be better than what we have now. The data brings good news and bad news.

The good news is, we have data, so Opportunity really is alive. (Maybe ODY is grieving for the pope instead.) The bad news is, the drive faulted out. Analysis shows that the first drive got closer to Voyager Crater than we'd planned -- a lot closer. Rather than being 10m or 15m away, we're right on the lip, with 8 degrees of tilt.

But that drive worked. Up to this point, the rover was happy and safe. (Not quite where we thought it would be, but happy and safe all the same.) But then the next sol's drive, the all-autonav continuation drive, kicked in. In the course of this drive, autonav climbed a little higher on the crater lip, hitting the max tilt limit of 12 degrees, which stopped the drive. It drove only about two meters.

Part of this is just due to a dumb misconfiguration. The autonav software has its own notion of what tilts to stay away from, and our default setting for this limit is 15 degrees. Thus, autonav doesn't know to avoid the 12-degree limit that stops driving. (Both limits are configurable; our mistake was to lower the max-tilt limit and not tell autonav.) If we'd lowered the autonav tilt limit as well, autonav would have known it should stay lower on the crater lip, and the drive might well have worked.

The other problem is that the first drive got much closer to the crater than we thought it would. This would be alarming even if the second drive had succeeded, and somebody (not me, thankfully) gets the responsibility for finding out why it happened.

So now we're trying to debug and recover from a drive failure, and we have no data. On a normal sol, this wouldn't be a problem -- we'd just clear the error, aim downhill, and step on the gas. But with no data, there's not a lot we can do. I work with Emily and Charles to re-prioritize the images already taken, so we'll get what we most need a little sooner. But the big problem is that we've gone from a fire hose to a drinking straw. We'll just have to wait.

As it happens, given the ODY situation, we don't want to drive until Wednesday or so anyway, at the earliest. So there's not any particular pressure. Just for the sake of it, I design a drive that would let us return to a clear zone and proceed to our next destination even if we get no further data, but we'll never send it. I just do it for the exercise.

I also realize one other piece of bad news. It's an unusual distinction, but for some reason, I happen to have crossed more kilometer boundaries with these rovers than anyone else. I don't know if I've done more total driving than anyone else (though I wouldn't doubt it), but I just happen to be on shift when the km number clicks over. Well, when the autonav drive faulted out, Opportunity was less than five meters from reaching the 5km mark. Someone else (Frank, I think) will get the glory this time. I mention this to the team, and Geoff Lake cocks an eyebrow at me. "Has anyone ever told you that you're really focused?" he asks. Only twice a day ....

Meanwhile, it occurs to me that we should exploit our fabulous position. We're poised on the lip of this crater; might as well take some pictures! But Charles Budney just shrugs. "Voyager is going to look like Viking," he says. "We'll take a low-res NAVCAM-360 and move on." That's a crime. This would make a spectacular full-color PANCAM panorama, but try as I might, I can't light a fire under the science team to do it, so I give up. But I'll tell you, it's a sad day when the engineers want science more than the scientists do.